Influence Of Enzymolysis Degree On Nuclear Structure And Induction Ability Of Whey Protein Nanofibers

Protein nanofiber polymer is a kind of linear polymer with excellent properties and stable structure.Due to its extreme aspect ratio,good viscoelasticity and other outstanding properties,it can effectively improve the product performance and the improvement degree of this performance is unmatched by conventional protein polymerization structure.In recent years,nanofiber polymer has become a research hotspot in the field of food applications.Whey protein nanofiber polymers can be formed by the spontaneous assembly of whey protein isolate under the conditions of low p H,low ionic strength,high temperature and long time heating,but this spontaneous assembly mode greatly limits the application of protein nanofiber polymers.Different from spontaneous assembly,nucleus induction can significantly shorten the fiber formation time and increase the fiber mass.And the team's previous research found that after the fibrous nucleus were treated with alkaline protease(2 h),the ability of inducing whey protein to form fibrous polymer was improved,which indicated that enzymatic hydrolysis could improve the ability of inducing fibrous nucleus.However,there is a lack of relevant research reports.Therefore,in this project,we continue to use enzymatic hydrolysis method to explore the effect of different degree of enzymatic hydrolysis on the induction ability of two kinds of fibrous nucleus.The difference of enzymatic hydrolysis ability between different fibrous nucleus was analyzed by analyzing the anti enzymatic hydrolysis ability and the retention rate of fibrous nucleus structure.The influence of the degree of enzymatic hydrolysis on the ability of nuclear induction was analyzed from the perspective of polymerization kinetics and driving force.Time of flight mass spectrometry,infrared spectroscopy and X-ray diffraction were used to study the relationship between the degree of enzymolysis and the core structure of fiber,and the relationship between the degree of enzymolysis,the change of nucleus structure and the inducing ability was discussed from the structural level.The results are as follows:(1)Difference of hydrolysis ability of different whey protein fibers:Compared with the raw material WPI,the two kinds of fibrous nucleus have a certain degree of anti enzymatic ability,and the secondary nucleus is stronger than the homogeneous nucleus.In time of flight mass spectrometry,the two kinds of fibrous nucleus showed unique characteristic peaks near 2083 Da,2197 Da and 2916 Da.Enzymatic hydrolysis lead to a rapid decrease in the intensity of characteristic peaks of homogeneous nucleus and secondary nucleus.In terms of particle size,the particle size of cellulose core after enzymatic hydrolysis was higher than that of raw material WPI under the same hydrolysis conditions,and compared with homogeneous nucleus,the larger particle size accounted for more in the secondary nucleus hydrolysate.From the results of fluorescence intensity of Th T,it can be seen that enzymatic hydrolysis will destroy the cross-?-sheet structure in the nucleus.However,compared with the homogeneous nucleus and raw material WPI,the particle size of the secondary nucleus hydrolysate was larger,the resistance to enzymatic hydrolysis was stronger,and reserved more cross-?-sheet structures.(2)Effect of enzymatic hydrolysis on the induction ability of homogeneous and secondary nucleus:The effect of enzymolysis on the ability of nucleus induction varies with the type of nucleus.Enzymatic hydrolysis can weaken the induction ability of homogeneous nucleus.When the degree of hydrolysis was 14.63%,it still has the ability of inducing,and the fluorescence intensity was 1.04 times higher than that of the spontaneous way,however,further enzymatic hydrolysis resulted in the loss of the induction of homogeneous nucleus hydrolysate.On the contrary,the ability of secondary nucleus induction was first increased and then decreased by enzymolysis,and moderate enzymolysis was beneficial to enhance the ability of secondary nucleus induction and the ability of secondary nucleus induction was the strongest when the hydrolysis time was 4 h(the degree of hydrolysis was 22.66%),and compared with WPI spontaneous assembly method,the induction ability of WPI increased by 14.34%,compared with the unhydrolyzed secondary nucleus,the induction ability was increased by 9.47%.(3)Effect of enzymatic hydrolysis on the mode of nucleus induced polymerization:As for homogeneous nucleus,when the degree of enzymatic hydrolysis was less than 14.63%,nucleus induction will prolonged t_lagand t_0.5max,and decreased(df/dt)_maxand f_max.As for secondary nucleus,when the degree of enzymolysis was less than 22.66%,nucleus induction had no significant effect on t_lag,but shortened t_0.5max,increased(df/dt)_maxand f_max.However,compared with WPI spontaneous assembly method,the kinetic parameters induced by nucleus hydrolysate(the degree of hydrolysis mentioned above)were still faster than that of WPI spontaneous assembly,the two kinds of nucleus still have inducing ability.(4)Effect of enzymolysis degree on the structure of fibrous nucleus:Enzymatic hydrolysis will destroy the basic building units of fiber polymer?-sheet structure,but when the retention rate of?-sheet structure in the secondary structure of fibrous nucleus was more than 30%,two kinds of nucleus had inducing ability,and the core structure of the fiber still exists.If the time of enzymolysis is prolonged,the parallel arrangement of cross-?-sheets lamellae in the nucleus structure of the fiber will be destroyed first,and the orderly stacking of cross-?-chains will be destroyed gradually,resulting in the loss of the nucleus structure of the fiber,and the nucleus hydrolysate has no induction ability.In conclusion,the loss of cross-?-sheets lamellar structure in the fiber core structure may lead to the gradual weakening of nucleus induction ability,and compared with the raw material WPI and homogeneous nucleus,enzymatic hydrolysis has less damage to cross-?-sheets lamellae structure in the secondary nucleus,relatively speaking,the secondary nucleus structure is more robust.